In Patent Document 1, a synthetic resin-made sliding bearing is proposed which includes a synthetic resin-made lower casing, a synthetic resin-made upper casing superposed on this lower casing, and a synthetic resin-made sliding bearing means interposed between the upper and lower casings, the synthetic resin-made sliding bearing comprised of an outer resiliently sealing means disposed on an outer peripheral side between the upper and lower casings and an inner resiliently sealing means disposed on an inner peripheral side between the upper and lower casings. In Patent Document 2, a synthetic resin-made sliding bearing is proposed which includes a synthetic resin-made lower casing, a synthetic resin-made upper casing superposed on this lower casing, and a synthetic resin-made thrust sliding bearing member disposed in a space between the upper and lower casings, the synthetic resin-made sliding bearing comprised of an outer sealing means disposed on an outer peripheral side in the space between the upper and lower casings and an inner labyrinth sealing means disposed on an inner peripheral side in the space between the upper and lower casings. In Patent Document 3, a synthetic resin-made sliding bearing is proposed which includes a synthetic resin-made lower casing, a synthetic resin-made upper casing superposed on this lower casing, and a synthetic resin-made sliding bearing means interposed between the upper and lower casings, the synthetic resin-made sliding bearing comprised of a resiliently sealing means which is disposed in such a manner as to cover an outer surface of the lower casing and which seals outer and inner annular openings of a space between the upper and lower casings at both annular end portions. In Patent Document 4, a synthetic resin-made sliding bearing is proposed which includes an upper casing having an annular lower surface, a lower casing which is superposed on this upper casing so as to be rotatable about an axis of the upper casing and has an annular upper surface, and an annular thrust sliding bearing piece disposed in an annular space between the annular lower surface and the annular upper surface, the sliding bearing comprised of a sealing means disposed on at least one side of an outer peripheral side and an inner peripheral side of the annular space. Furthermore, in Patent Document 5, a synthetic resin-made sliding bearing is proposed which includes a synthetic resin-made upper casing having an annular lower surface, a synthetic resin-made lower casing having an annular upper surface, and a thrust sliding bearing piece disposed in an annular gap between the annular lower surface and the annular upper surface.